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In Reply to: Re: And a good opinion at that! posted by bobbyj on December 12, 2006 at 10:06:33:
We audio geeks are a funny breed. Somebody else would read your post and say the guy knows what he likes so why does he want to change? Sadly I understand why:)Notice that Gary has no power supply shown. Hmmm, could it be that the power supply isn't the important part? Instead I'd point to a few big items. Number one, just about everything has an active load. Number two, pains are taken to keep the voltages where they should be on stages that operate with constant current. Number three and the biggie IMHO, the circuit strives to keep audio circuits in a tight loop and return them locally rather than through a common ground and/or power supply. I think this is key and I see it happening time and again on better designs. Moreso in push pull than SET but still there is a common thread.
A choke, transformer, or a CCS helps "isolates" the circuit from the power supply. Ditto on the parafeed with the cap to cathode on 300B. I suggest you look more into these areas. I think parafeed may bring you some of the improvments in bass you seek.
With regards to the low dcr stuff....I have looked into it a bit and in fact dcr has little if anything to do with it. The main interesting point is the voltage on the first cap is greater than 1.4 times the secondary voltage. Circuit values are critical. I would not advise the design for anyone other than an expert who was looking for a challenge.
A little time spent with Duncan's PSUD will show a very low DCR supply rings like crazy. If you are interested in the low dcr thing and understanding it better search on "flywheel" over at tube diy.
Follow Ups:
Thanks Russ.After checking back in on Gary's schematic, I realize I already ground this way. Isn't this called "star" ground? I think I'll park the ultra low dcr concept for the moment, and try to take the circuit a step further.
Since the primary of an SE output designed for standing current
is in itself "a choke", the advantage of parafeed's "isolation" is then to A: "use a bigger choke" (or CCS) and B: to loose the "problems" of standing DC current in the OPT , is that rightish? Gary's cap seems to be in the plate circuit (rev. 3). I guess I've seen it done both ways, what's the difference? I wouldn't know how to design a CCS, but I'd like to learn.
On a tangent, having played around briefly with a 26 once, it had a profound "darkness" to it, that I thought was kinda refreshing, yet after a little while, I realized (perhaps the Rp) it was just "missing" a lot of HF noise and music simultaneously.
Gary's comment about his amp "not loosing composure even when things get wild" is, I guess what I'm after. Most of my listening is less "wild" stuff, so what I have already "stays composed", mostly, but sometimes when wild stuff comes, it does seem to "not quite keep up". Not distort exactly, just, I'm not sure what. This is one of the things I'd like to "fix". Maybe it's also partially a power issue, but I'm not ready to go dc filaments to get more power, although I would if...
I would prefer to exhaust the potential of a bottle that I can operate with AC filaments first. Has someone developed a CCS plate load for a 2A3? that's "public" knowledge or is there a book on designing CCS's? or?
Is this the right forum for this or is tube/ DIY more appropriate?
The advantage of parafeed is allowing you to close the loop locally. The output tube's current is confined to the primary of the transformer and it returned directly to the tube's cathode. In a normal connection the return must be through the mian power supply cap. Hopefully the parafeed cap would be smaller and of higher quality.Putting the cap "on top" keeps the DC voltage out of the transformer. Not having to have the transformer handle either DC current, so no air gap required, as well as no high voltage DC, so not near the insulation required, can allow for a better and cheaper transformer. There are trade offs but considering your comments I think it is an area for you to consider.
Gary and Bottlehead sell CCS boards. The manual alone for the Bottlehead CCS is good reading and will explain a lot.
DC filaments wouldn't give you more power. You might be thinking of fixed bias compared to cathode bias. I would stay with AC as long as hum wasn't a problem.
I have decided it is best to use a solid state amp for the low bass and bi-amp with an electronic crossover. Not asking a couple/few watt amp to handle the low bass cleans up the mids/highs and helps the amp "keep up" on more complex music. Of course YMMV.
Russ
PS Yes tube diy is a good place to ask. Just takes awhile to learn who's advice to follow:)
I like the idea of better cheaper transformer, and wonder what the trade offs are? When the plate is loaded only by the OPT and an "ultrapath" cap is in place from top of cathode to B+ side of primary, does this actually remove the signal from the PSU? When I say DC filaments for more power I meant the use of more powerful triodes that would have to have dc to be quiet enough, like 300B, not thinking that dc alone would do anything for power, I realize I wasn't clear. I will look into the CCS boards you recommend, thanks.
I saw an interesting circuit on page 888 of the red book RCA radiotron designers handbook, that used a single input with two outputs that seemed like an elegant simple way to do a biamped/crossover thing.
I have single full range speakers so I can't do that.
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